This is a rath, the Irish term for a type of ringfort, a circular or near-circular enclosure defined by an earthen bank and outer ditch that was the standard form of farmstead and family enclosure across early medieval Ireland, roughly from the sixth to the twelfth centuries. Tens of thousands once dotted the Irish landscape; many survive only as crop marks or place-name traces, which makes a reasonably intact example like this one quietly notable.

The earthwork at Garrandillon measures approximately 32 metres north to south and nearly 38 metres east to west, giving it a slightly elongated oval plan. The enclosing bank is well preserved in parts, with a crest width of around 2.6 metres and a base spread of 7 metres. Its height varies considerably: internally it rises only 25 centimetres to 1.3 metres above the enclosed ground surface, while externally it stands between 1.4 and 2.4 metres, a difference most pronounced on the north-west downslope side where the ground falls away and the bank would have presented a more imposing face to anyone approaching from below. Beyond the bank lies an outer fosse, the ditch that typically accompanied such enclosures, though here a considerable amount of bank material has slipped into it over time, making it appear narrower than its original 3.5-metre width. An entrance, roughly 1.6 to 2 metres wide, sits in the north quadrant, oriented downslope, which is a practical choice for drainage and daily movement. Cattle have worn down the bank somewhat in the southern and western sections, a common fate for earthworks still embedded in working farmland.